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T. A. EDISON. SPEAKING TELEGRAPH.

No 474,231. Patented May 3, 1892..

NITED STATES PATENT Ornren.

THOMAS A. EDISON, OF MENLO PARK, NEW JERSEY, ASSIGNOR TO THE IVESTERNUNION TELEGRAPH COMPANY, OF NElV YORK, N. Y.

SPEAKING-TELEGRAPH.

SPECIFICATION forming part of Letters Patent No. 474,231, dated May 3,1892.

Application filed July 20, 1877. (Model) Patented in England July 30,1877, No. 2,909; in Canada October 20, 1877, No. 8,026; in FranceDecember 19, 1877,110. 121,687; in Belgium January 11,1878,No.43,984; inAustria-Hungary January 15,1878; in Italy January 19. 1878,111). 9,791;in GermanyJanuary 23, 1878,N0.14,308; in fipain May 6,1878,a11di11Russia February 15 /27, 1882, No. 1,161.

To aZZ whom, it 77 0011] concern.-

Be it known that I, THOMAS A. EDISON, of Menlo Park, in the county ofMiddlesex and State of New Jersey, have invented an Improvement inSpeaking-Telegraphs, (for which I have obtained foreign patents in thefollowing countries: in Great Britain, dated July 30, 1877, No. 2,909;in France, dated December 19, 1877, No. 121,687; in Belgium, datedJanuary 11, 1878, No. 48,984; in Italy, dated January 19, 1878, No.9,791; in Spain, dated May 6, 1878; in Austria-l-lungary, dated January15, 1878; in Germany, dated January 23, 1878, No. 14,308; in Russia,dated February 15/27, 1882, No. 1,161, and in Canada, dated October 20,1877, No. 8,026,) of which the following is a specification.

The object of this invention is to transmit the human voice overtelegraphic wires for conversational purposes.

The invention consists in the use, in the circuit of aspeaking-telegraph transmitter, of one or more contactrpoints formed ofsemiconductors, such as plumbago, peroxide of lead, and other oxides andconducting ma terial.

Figure 1 shows the transmitter and receiver. A is the resonant chamber,over the end of which the diaphragm is stretched, either side of whichmay be made heavier in the center by a small weight if great amplitudeis required of the diaphragm; b c are the two contact-springs, havingpoints made of (30111- pressed plumbago, mixed, preferably, withgrim-rubber; but any substance not liable to rapid decomposition may beused. These points face each other on the opposite side of the diaphragmand make contact with platina disks secured to the diaphragm. Thespring 1) passes through a hole or small slot in the side of thetransmitter. 2 and 3are themain batteries. The battery 2 has zinc to theline or point e and the battery 3 has copper to the line or spring 3).When the springs c and b are adjusted so as to make contact with thediaphragm equally, no current passes to the line; but when the diaphragmis vibrated its movement to one'side say c-causes a greater pressureupon the plumbago on that spring and a lessening of the pressure on theplumbago on b. Hencethe balance of the batteries 2 and 3 will bedestroyed. 2 being given the advantage will send a negative current toline. the battery-currents will again neutralize each other. Thevibration of the diaphragm to the other side causes the pressure to bereversed and the battery 3 will send a positive current to the line. Asplumbago decreases and increases its resistance enormously under slightchanges of pressure, it follows that the strength of the electric waveswill be in proportion as the speakers voice is strong or weak.

In Fig. 2 isshown the contact spring, which I prefer to use instead of cand b, which are used merely to assist in explaining the operations moreclearly. 5 is a U-shaped spring secured to the screw 8, which isadjusted back and forward by the thumb-nut 9. 7 is the pillar holdingsuch screws. r is a piece of soft rubber or equivalent substance placedbetween the prongs of the spring 5. 6 is a wire or band, which serves tobind the prongs tightly against the rubber r, so as to prevent theprongs acting as a tuning-fork and transmitting harmonic vibrations notdesirable. 10 is the plumbago cOnt-actpoint. The object of the U-springand rubber is to present a semi-rigid point for contact, so as toprevent a rebound and allow of a slight yield when the plumbago ispressed by the diaphragm. D is the receiver, which consists of aresonant chamber of any suitable character, either a tube, as in Fig.3', or as a box, as at D, Fig. 1. fis a rigid arm secured to the box andis provided upon its extreme end with an adjustingscrew 7:. Near the endof the arm is secured a spring g, whose end rests upon thechemically-prepared paper upon the drum e. The under side resting uponthe paper is platinized. The screw hserves to increase and decrease thepressure of the platina spring upon the paper. When the paper is movedslowly by rotating the drum 6, the waves of electricity coming over theline pass through Upon the return of the diaphragm the arm f to theplatinized spring g; thence through the paper to the earth. If anegative current passes in the opposite direction, nearly all frictionbetween the platina plate and the paper ceases and the resonant boX ordiaphragm regains its normal position. hen the positive current passesthrough the same channel, thenormal friction of the paper is augmentedand the chemical surface, acting upon the platina, serves to give amovement to the resonant box. Thus the mechanical force applied to movethe chemical surface acts with the electric current to produce thevibration of the resonant chamber. The principle of this method ofobtaining motion by electrochemicaldecompositionisdescribedinmyLettersPatent No. 158,787, granted January 19, 1875. To facilitate thedischarge of electricity from the receiving apparatus, it may be shuntedwith an electro-magnet.

Fig. 4: shows the devices which may be employed to rotate the drum 6 ina noiseless manner, so as to prevent interference with the weak hissingconsonants, which form a part of ordinary conversation. p is a worm, and0 the wheel for revolving the roller 6. t is a. universal jointconnecting to the shafts, the object of the shaft being to carry theactuating-handle to the right side of the machine andthe paper-carryingdevices to the left-hand side. 4) is a spring, which serves to press therubber wheel against the under surface of the wheel at, which also maybe covered with rubber. to is the handle by which to rotate the disk 16,shaft 5, worm p, and roller 6.

The mouth of the speaking-tube may be {closed except a horizontal slot,through which the vibrations of the voice pass to the diaphragm ortympan, the object of the slot being to increase the power of thehissing consonants; also, the point Z) may-be dispensed with on veryshort lines.

In this specification no claim is made to the .use of a spring forcarrying one of the electrodes, since thatinvention forms thesubjectmatter of an application, Serial No. 192,456,

filed as a division hereof.

THOS. A. EDISON.

Witnesses.-

GEO. T. PINCKNEY, WILLIAM G. MOTT.

